The present invention relates to press rolls.
In particular, the present invention relates to press rolls for treating sheet material such as paper and suitable for use in the calender or press section of a paper machine.
The present invention relates in particular to a press roll having a shaft surrounded by a shell which is spaced from and rotatable with respect to the shaft, the shell and shaft defining between themselves a gap in which is located a structure capable of receiving a pressurized fluid for controlling the deflection of the shell.
Press rolls of the above general type are known. The known rolls include an inner shaft and an outer shell surrounding and rotatable with respect to the shaft, and while there is a pressure zone extending between the shaft and shell, it is not possible with the previously known constructions to vary the pressure acting on the shell, particularly longitudinally of the roll. In this connection reference may be made to the German Federal Republic Pat. No. 1,026,609.
Also known in the art is a press roll for achieving a uniform pressure and having between the shaft and shell a component in the form of a cushion-like hollow member filled with a pressurized fluid and retained in place by shoulders at the edges of a recess formed in the shaft. The outer surface of the cushion-like hollow member engages a slip membrane against which the inner surface of the shell slides. A construction of this type is disclosed in German Federal Republic Pat. No. 1,111,932.
Also, there is a known press roll having its shaft provided with radially directed pressure cylinders in which pistons operate, with suitable slide shoes engaging the inner surface of the shell for receiving the forces provided by the pistons. A structure of this type is disclosed in German Federal Republic Pat. No. 1,193,792.
Also, a previously known press roll has formed in its shaft a longitudinal pressure groove in which a bar slides to operate as a piston, with a slide piece being provided and having a length equal to that of the shell, this latter piece being rigid and non-rotatably fixed to the shaft and transmitting the force to the inner surface of the shell. This pressure groove may be divided into compartments by means of partitions, with the bar which serves as a piston being correspondingly subdivided into sections so that different pressures may be achieved in the compartments, respectively. A construction of this type is disclosed in U.S. Pat. No. 3,119,324.
The known constructions of the above type suffer from several drawbacks. For example the shafts of such constructions are not as strong as desired because of the fact that such shafts require hollow interior portions to accommodate pressure-controlling structure. Also, it is not possible with the previously known constructions to achieve the desired pressure controls with the precision which is desired and in such a way that the shell can have different pressures distributed longitudinally thereof.
Moreover, the sealing structure utilized in the conventional press rolls is exceedingly complex, often requiring separate seals on the one hand to extend longitudinally of a pressure zone and on the other hand to be situated at the ends of the pressure zone.